/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.state;



import com.bff.gaia.unified.sdk.annotations.Experimental;

import com.bff.gaia.unified.sdk.annotations.Experimental.Kind;

import com.bff.gaia.unified.sdk.transforms.Combine;

import com.bff.gaia.unified.sdk.transforms.GroupByKey;



/**

 * A {@link ReadableState} cell that combines multiple input values and outputs a single value of a

 * different type.

 *

 * <p>This generalizes {@link GroupByKey} and {@link Combine} styles of grouping.

 *

 * @param <InputT> the type of values added to the state

 * @param <OutputT> the type of value extracted from the state

 */

@Experimental(Kind.STATE)

public interface GroupingState<InputT, OutputT> extends ReadableState<OutputT>, State {

  /**

   * Add a value to the buffer.

   *

   * <p>Elements added will not be reflected in {@code OutputT} objects returned by previous calls

   * to {@link #read}.

   */

  void add(InputT value);



  /**

   * Returns a {@link ReadableState} whose {@link #read} method will return true if this state is

   * empty at the point when that {@link #read} call returns.

   */

  ReadableState<Boolean> isEmpty();



  @Override

  GroupingState<InputT, OutputT> readLater();

}